Boron
Boron is a chemical element on the periodic table of elements that has the symbol B and atomic number 5, its mass is 10,811. It is a trivalent, semiconductor, metalloid element that exists abundantly in the mineral borax. There are two allotropes of boron; amorphous boron is a brown powder, but metallic boron is black. The metallic form is hard (9.5 on the Mohs scale) and is a poor conductor at room temperature. It has not been found free in nature.
Features
Boron is an element with electron vacancies in the orbital; For this reason, it shows a pronounced appetite for electrons, so that its compounds often behave like Lewis acids, reacting quickly with substances rich in electrons.
Among the optical characteristics of this element, the transmission of infrared radiation is included. At room temperature, its electrical conductivity is small, but it is a good conductor of electricity if it is at a high temperature.
This metalloid has the highest tensile strength among the known chemical elements; the arc-molten material has a mechanical resistance between 1,600 and 2,400 MPa.
Boron nitride, an electrical insulator that conducts heat as well as metals, is used to obtain materials as hard as diamond. Boron also has lubricating qualities similar to graphite and shares with carbon the ability to form molecular networks through stable covalent bonds.
Reactivity
In its compounds, boron acts as a nonmetal, but it differs from them in that pure boron is an electrical conductor, like metals and like graphite (carbon). When red, it combines directly with nitrogen to form boron nitride (BN), and with oxygen to form boron oxide (B2O3). With metals it forms borides, such as magnesium boride (Mg3B2). More extraordinary is the anomalous similarity of boron hydrides to the corresponding compounds of silicon and carbon. There are various boron hydrides known under the generic name of boranes, all of which are toxic and have a very unpleasant odor. In flame tests it produces a characteristic green coloration.
Uses
Used to make borosilicate glass (eg Pyrex) and enamels, mainly for cookware. It is also used to obtain special steels, with high impact resistance, and other alloys. Due to its great hardness it is used, in the form of carbide, to make abrasives. Boron has several important applications in the field of atomic energy. It is used in instruments designed to detect and count neutron emissions. Because of its great neutron absorption capacity, it is used as a control damper in nuclear reactors and as a constituent material for neutron shields. Dilute boric acid is used as an antiseptic for the eyes and nose. In the past, boric acid was used to preserve food, but this use has been prohibited due to its harmful effects on health. Boron carbide is used as an abrasive and alloying agent.
Applications
The most economically important boron compound is borax, which is used in large quantities in the manufacture of fiberglass insulation and sodium perborate. Other uses include:
- Boro fibers used in special mechanical applications, in the aerospace sphere, achieve mechanical resistances of up to 3600 MPa.
- The buffer is used in pyrotechnic fires for its green color.
- Boric acid is used in textiles.
- Boro is used as a semiconductor.
- Boro compounds have many applications in organic synthesis and in the manufacture of borosilicate crystals.
- Some compounds are used as wood preservatives, being of great interest their use for their low toxicity. and ReB2
- B-10 is used in the control of nuclear reactors, as a shield against radiation and neutron detection.
- Boro rows are easily oxidized by releasing a lot of energy so their use as fuel has been studied.
- Currently, the research is being conducted in the production of hydrogen-like fuel with the interaction of water and a boro hydrouro (such as NaBH4). The engine would work by mixing the boro hydrogen with water to produce the hydrogen as needed, so that they solve some difficulties of applying the hydrogen safely in the transport and its corresponding storage. Research is taking place at the University of Minessota (United States) and the Institute of Science in Rehovot (Israel).
Training
According to the Big Bang theory, at the origin of the Universe we find elements H (hydrogen), He (helium) and Li-7 (lithium-7), but B, the fifth element of the periodic table, does not It has a noticeable presence. Therefore, in the condensation of the first nebulae, fundamentally H stars are formed with a portion of He (helium) and Li-7 (lithium-7), in which the different processes of element formation take place (Proton chain -proton, triple a process and CNO cycle). But in none of them is boron formed as a product, since at such temperatures (on the order of 107-108k) it reacts at a higher rate than it is formed. Boron is also not formed during the neutron capture process, which results in atoms of high atomic mass. The B is formed in a process called cosmic ray spallation, which consists of the breakage of nuclei heavier than boron due to the bombardment of cosmic rays. Because this process is so rare, the cosmic abundance of boron is very small.
History
Boron compounds (from Arabic buraq and eastern from Persian burah) have been known for thousands of years. In ancient Egypt mummification relied on natron, a mineral that contained borates and other common salts. Borax crystals were already used in China around 300 BC. C., and in ancient Rome boron compounds in the manufacture of glass. From the 8th century, borates were used in gold and silver refining processes.
In 1808 Humphry Davy, Gay-Lussac and L. J. Thenard obtained boron with a purity of approximately 50%, although none of them recognized the substance as a new element, which Jöns Jacob Berzelius would do in 1824. Pure boron was first produced by American chemist W. Weintraub in 1909.
Getting
Boron in its circular form is not found in nature. The major source of boron is borates from evaporitic deposits, such as borax and, less importantly, colemanite. Boron also precipitates as orthoboric acid H3BO3 around some sources and volcanic fumes, giving sasolites. Natural boron ores are also formed in the solidification process of silicate magmas; these deposits are pegmatites.
The most important deposits of these ores are the following: borax deposits are found in California (USA), Tincalayu (Argentina) and Kirka (Turkey). From colemanite in Turkey and in Death Valley (USA). Sasolites in geologically active sites in the Larderello region (Italy). It is commercially sold as Na2B4O7 10 H2O or pentahydrate, it is known as Borax.
Pure boron is difficult to prepare; the first methods used required the reduction of the oxide with metals such as magnesium or aluminum, but the resulting product was almost always contaminated. It can be obtained by reduction of volatile boron halides with hydrogen at high temperature.
| 1. | Turkey Turkey | 2.400 |
| 2. | Chile Chile | 400 |
| 3. | China China | 250 |
| 4. | Bolivia Bolivia | 200 |
| 5. | Germany Germany | 120 |
| 6. | Peru Peru | 111 |
| 7. | Russia Russia | 80 |
| 8. |  Argentina | 71 |
Source: USGS. NOTE: No data has been published for the United States.
Allotropes
Boron presents a multitude of allotropic forms that have a regular icosahedron as a common structural element. The ordering of the icosahedrons can be in two different ways:
- Union of two icosaedros by two vertices, through normal covalents B - B (Figure 1).
- Union of three icosaedros by three vertices, through a link of three centers with two electrons (Figure 2).
Figure 1.
Figure 2.
Within these possible unions, in crystalline boron the icosahedrons can associate in various ways to give rise to the corresponding allotropes:
- Tetragonal Boro (T - 50): made up of 50 atoms of embroidery by cell unit, which are four icosaedrical units joined together by some B-B and two elemental borons that act as a tetraetric union between icosaedros. It has a density of 2.31 g/cm3.
- Alpha Romboiric Boro (R - 12): it is formed by foils of icosaedros joined in parallel. Intralaminar unions are made through links of three centers, while interlaminar unions are produced through links of two centers. The density of this type of embroidery is 2.46 g/cm3, and has a light red colour.
- Romboiric beta (R - 105): formed by twelve icosaedros B12 ordained in icosae manner around a central unit of B12I mean, B12(B)12)12. It has a density of 2.35 g/cm3.
Abundance in the universe
The abundance of boron in the universe has been estimated at 0.001 ppm, a very small abundance that together with the abundances of lithium, molybdenum and beryllium forms the quartet of "light" rarest in the universe, the rest of the elements of the first four periods—up to and excepting arsenic—are at least ten times more abundant than boron (except for scandium and gallium, which are about five times more abundant than boron).
Distribution of boron in the Solar System
Boron has a high melting point (2348 K), therefore it is a refractory element that condenses and accretes in the early stages of the condensation of a nebula. This fact places it in the Internal Solar System, since during the phase of the Sun known as T-Tauri (initial phase of the life of a star, during which it emits solar wind with great intensity) the solar wind produces an effect of drag on the masses of particles that orbit around it, dragging the less dense ones to the outside (volatile elements) and remaining the most dense ones (refractory elements). In other words, we will find boron on the rocky planets that make up the Inner Solar System, but the abundance will drop a lot on the gaseous planets of the Outer Solar System.
Distribution of boron in meteorites
Meteorites (chondrites and achondrites) show boron concentrations around 0.4 and 1.4 ppm respectively. These concentrations are substantially higher than those in the universe, since other elements that are more volatile than boron are dispersed through space in the gas phase (atmophilic elements such as hydrogen and helium, which are neither in the form of solids nor do they condense), or forming "clouds" of gas around solids due to a gravitational field, or in the form of an atmospheric fluid. The abundance of these elements in the gas phase represents a good part of the abundance of matter in the universe, and if we consider that meteorites (either chondrites or achondrites), being solid, do not have these elements, or do not have them in abundance, then the abundance of the other elements will be increased. The difference between the abundances of chondrites and achondrites is understood in the fact that boron is an exclusively lithophilic element, that is, it has a preference for being incorporated into the silicate liquid phases. Chondrites are rocks or samples of extraterrestrial rock that have not gone through a differentiation process, that is, they have not melted or separated into silicates, metals, and sulfides. The achondrites, on the other hand, are samples of silicate rock, coming from differentiated masses, for this reason their abundance of boron is greater than in the chondrites.
Boron in the earth's crust
The estimated concentration of boron in the Earth's crust is 10 ppm, and its mass is 2.4 × 1017 kg. Currently it is known that boron is much more abundant in sedimentary rocks (300 ppm) than in igneous rocks (3 ppm). This difference is a consequence of four characteristics: boron is sublimable, the non-preference of boron for molten phases (incompatible element), its high mobility in the aqueous phase and its strong affinity for clay minerals (lithophilic element).
Boron reaches the earth's crust through different routes, and these are atmospheric precipitation, which contains small amounts of boron in solution; and volcanism and similar geological activity, which release molten rock with varying concentrations of boron. There are also flows from the ocean to the oceanic crust in the form of sedimentation and diagenesis. The ways out of the curtical boron are erosion and plate subduction processes.
Boron tends to concentrate in the residual phases of the molten part, the elements that make up the magma mass solidify depending on their melting point and their compatibility with the solid phase, thus, in the successive stages After solidification, the concentration of incompatible elements (including boron) increases in the magma, until finally we have a liquid made up of incompatible elements that end up solidifying. These deposits of incompatible elements are what we know by the name of pegmatites. Due to this fact, boron concentrations are relatively low in basalts (6-0.1 ppm) and higher in more crystallized rocks such as granite (85 ppm), although high boron concentrations are also found in granites derived from rich sedimentary rocks. in boron. Pegmatites can contain boron concentrations of 1360 ppm.
During the deterioration of underwater rocks, igneous rocks degrade and form clay minerals that adsorb boron from seawater, thereby enriching the rock mass with boron.
Basalts on magmatic islands tend to be boron-enriched; This enrichment is attributed to the dehydration of the subducted rock blocks, rich in boron adsorbed by clay minerals. The boron-rich fractions take part in the melting process and the resulting volcanic rocks (andesites and diorites) are consequently boron-enriched. Clay minerals (such as illites, smectites, and montmorillonites) incorporate boron from water both by adsorption and as a substitution element in the structure. Sedimentary rocks from the oceans tend to contain more boron than fluvial sedimentary rocks, since seawater contains a higher concentration of boron than inland waters. Boron is adsorbed only at temperatures below 40 °C, at higher temperatures (>150 °C) it can be released from the mineral, therefore, during metamorphism of sedimentary rocks much of the adsorbed boron is released into the water, and if metamorphism is further increased, boron as a substituent element is also released, therefore metamorphosed sediments tend to contain vastly lower concentrations of boron than equivalent unmetamorphized sedimentary rocks.
The main minerals in which we find boron are mostly evaporitic rocks, like borax, highly soluble in water; the colemanita; kernite (a partially dehydrated form of borax) and ulexite. There are also important boron minerals in the form of igneous rock deposits, datolite, plover and elbanite, these minerals are classified in the group of borates (inorganic salts composed of boron and other ions), except for the last two minerals mentioned., which belong to the group of tourmalines, which appear especially in veins of the pegmatitic type.
Boron in the hydrosphere
Boron is found in seawater at concentrations estimated at 4.6 ppm and in a mass of 5.4 × 1015 kg. It is found as a component of two hydrated molecules; the B(OH)3 trigonal and the B(OH)4- tetrahedral. The ratio of the two forms depends on the pH of the seawater and the equilibrium between the concentrations of the two forms is found at a pH of 8.7-8.8, in more basic media the tetrahedral form predominates and in more acidic media the tetrahedral form predominates. trigonal. Due to the long residence time of boron in seawater (25 million years), the concentrations of B(OH)3 and B(OH)4- do not vary significantly in different oceans. Boron reaches the hydrosphere from the continents through the water cycle and through rock erosion processes, and from the oceanic crust through hydrothermal circulation, and also comes from atmospheric precipitation.
Sources of boron in Chile
Relatively scarce in nature, boron occurs in abundance in the rivers of northern Chile, especially in the Atacama and Antofagasta region, where the volcanic nature of the watersheds are rich in borates. In these regions it is possible to find dissolved boron in the order of 2 to 12 ppm, usually between 1 and 4 ppm. The seawater in these areas contains between 4-5 ppm of dissolved boron and its levels rise at the mouths of the rivers, especially in periods of volcanism.
Also, the borax industry is evident in these regions.
Boron in the atmosphere
The atmosphere contains about 2.7 × 108 kg of boron. This is found in the troposphere in a gaseous state in 97%, the remaining 3% is in a solid state in the form of particles. The residence times that are considered for tropospheric boron in its gaseous form are from 19 to 36 days, for particulate boron they are from 2 to 6 days. Due to these low residence times, boron concentrations are variable at different points in the atmosphere. Boron reaches the atmosphere through the evaporation of seawater, then it can return to the oceans or continents by precipitation. It becomes very harmful to the people and living beings that live here.
Boron in plants
For plants, boron is an essential nutrient. It seems to have a fundamental role in maintaining the structure of the cell wall (through the formation of cis-diol groups) and membranes. It is an element that is not very mobile in the phloem, therefore deficiency symptoms usually appear in young leaves and toxicity symptoms in mature leaves. An excess of boron is detrimental to some plants that are not very tolerant of boron, and can act on their veins, weakening them. In apple and pear trees, boron deficiency manifests itself in the fruits, with an internal malformation called "corky heart".
Isotopes
Two isotopes of boron are found in nature, 11B (80.1%) and 10B (19.9%). The results of their masses differ in a wide range of values that are defined as the difference between the fractions 11B and 10B and traditionally expressed in parts per thousand, in natural waters ranging from -16 to 59. There are 13 known isotopes of boron, the shortest lived isotope is 7B which decays via proton emission and alpha decay. It has a half-life of 3.5×10−22s. The isotopic fractionation of boron is controlled by the exchange reactions of the special compounds B(OH)3 and B(OH)4. Boron isotopes are also fractionated during mineral crystallization, during H2O phase changes in hydrothermal systems, and during hydrothermal alteration of rocks.
Precautions
Neither boron nor borates are toxic to humans and animals. The LD50 for animals is about 6 g per kg of body weight. Substances with LD50 above 2g are considered non-toxic. The minimum lethal dose for humans has not been established, but an intake of 4 g/day was reported without incident, and clinical doses of 20 g of boric acid for neutron capture therapy caused no problems. Some fish have survived for 30 minutes in a saturated boric acid solution and can survive longer in borax solutions. Borates are more toxic to insects than mammals. Borane and some similar gaseous compounds are very poisonous. As usual, it is not an element that is intrinsically poisonous, but its toxicity depends on the structure.
Boranes (hydrogen boron compounds) are toxic, as well as easily flammable and require special care when handling. Sodium borohydride presents a fire hazard due to its reducing character, and the release of hydrogen on contact with acid. Boron halides are corrosive.
Boron in human health
Scientifically, it has not been proven that boron is a substance considered essential in the human diet or that it is a dietary requirement in vertebrates and invertebrates, or at least of the same importance that it occupies in vegetables.
The human body contains at least 0.7 mg per kilo of boron obtained from the consumption of water and vegetables. A human consumes in his daily intake about 0.8 to 2.5 mg of boron per kilo of weight without showing any symptoms for this. Crash diets of 5 g per day can cause nausea, diarrhea and vomiting, some literature suggests that 20 g per day of boron may be fatal in sensitive organisms but this has not been proven.
The German biochemical researcher: "Walter Last", in his study published under the name: " The Borax conspiracy: The end of the cure for osteoarthritis", has carried out extensive research associating the lack or deficiency of this trace element in the development of osteoarthritis, arthritis, rheumatoid arthritis, osteoporosis, ect, among many other ills. On the contrary, he has discovered that the intake of boron in adequate proportions helps to eradicate these evils, becoming a regenerated cell; since it is essential for the metabolization of calcium and magnesium: https://desdepachamama.com/archivos/La-conspiracion-del-Borax-de-Walter-Last-Bioquimico-e-investigador.pdf
Other publications estimate that this element should be considered at the trace element level as essential for the metabolism of calcium, copper, magnesium and nitrogen fixation: http://www.elmorrocotudo.cl/admin/render/noticia/8931
The WHO has estimated that the acceptable level of boron in water is 2.4 ppm. In Europe, local standards are between 1 - 2 ppm and in Canada, 5 ppm.
Boron abatement
Due to its nature, boron is not easy to remove from aqueous matrices. Classic coagulation, sedimentation and even reverse osmosis techniques are not satisfactory. Some research entities such as Fundación Chile have indicated that the application of ion exchange resin systems in conjunction with zeolites and activated carbon are much more promising as ways to reduce this element.